1. Field of the Invention
The present invention relates to devices for providing a fluid-tight seal or block in a tubular member, such as a conduit or a nozzle or the like. The invention has particular application to providing a dam or seal in the primary fluid nozzles of a nuclear steam generator.
2. Description of the Prior Art
The present invention is an improvement of the nozzle dam disclosed in the copending U.S. application Ser. No. 651,419, the disclosure of which is incorporated herein by reference. It has been found that in that nozzle dam the seal membrane or diaphragm on the upper or inner seal, i.e., the one closest to the inside of the plenum, becomes flexed and stressed in use as a result of the pressure differential across the seal. This flexure and stressing of the diaphragm is the result of the fact that, since the diaphragm is disposed on the low pressure side of the upper seal, it is essentially unsupported whereas, in contrast, the membrane on the lower seal is supported by the foldable seal plate or base which prevents undue flexure and stress of that lower diaphragm.
The membrane cannot, however, be simply moved to the high pressure side of the seal, since this would prevent folding of the seal plate sections, which are hinged on the low pressure side, so that the sections will not tend to fold up when the inner seal is urged by the pressure differential into wedge-fitted engagement with the frustoconical portion of the inner surface of the nozzle.